Smart sensor system using an electroactive polymer

Abstract

A system for measuring a solution pH includes a potentiostat with a working electrode made of an electro-conductive solid polymer transducer, an input to receive the potential to be applied between the working electrode and a reference electrode, and an output to transmit a signal representative of the current flowing between a counter electrode and the working electrode, the three electrodes being immerged into the solution. The system further includes a digital processor connected to a digital to analog converter for generating the potential to be applied between the working and the reference electrodes; and to an analog to digital converter for receiving a digital value representative of the current. The digital processor is adapted to modify the potential to maintain the current inside a predetermined range such that the potential is representative of the solution pH when the current is inside the predetermined range.

The invention claimed is: 
     
       1. A method for measuring a solution pH with a potentiostat, said potentiostat comprising a working electrode made of an electro-conductive solid polymer transducer, an input configured to receive an input signal which provides a working potential to be applied between said working electrode and a reference electrode of the potentiostat, and an output configured to transmit an output signal indicative of the magnitude of the current flowing between a counter electrode of the potentiostat and said working electrode, said three electrodes being immerged into said solution, said method comprising:
 generating the input signal; 
 sensing the output signal; 
 modifying the input signal and said working potential so as to maintain said output signal inside a predetermined range, wherein the input signal potential is representative of the solution pH when said output signal is maintained inside said predetermined range. 
 
     
     
       2. The method of  claim 1 , wherein said method is implemented in a computer software product stored on a recording media as a set of instructions configured to enable a computer to practice the method when the computer executes said set of instructions. 
     
     
       3. A system, comprising:
 an electrode cell including a working electrode, a reference electrode and a counter electrode, wherein the working electrode is made of an electro-conductive solid polymer transducer; 
 a first circuit configured to apply a working potential to the electrode cell in response to a control signal; 
 a second circuit configured to sense a current flowing between the counter electrode and the working electrode when the working electrode, reference electrode and counter electrode are submerged in a solution under test; and 
 processing circuitry including:
 an analog to digital converter coupled to an output of the second circuit and configured to convert the sensed current to a digital current value; 
 a digital to analog converter coupled to an input of the first circuit and configured to convert a digital signal to said control signal; and 
 a processor configured to implement a feedback loop responsive to the sensed current which modifies the digital signal and said working potential so as to maintain the digital current value within a range. 
 
 
     
     
       4. The system according to  claim 3 , wherein the working electrode is made of polyaniline or polypyrrole. 
     
     
       5. A system for measuring a solution pH, comprising:
 a potentiostat comprising a working electrode made of an electro-conductive solid polymer transducer, an input configured to receive an input signal which provides a working potential to be applied between said working electrode and a reference electrode of the potentiostat, and an output configured to transmit an output signal indicative of the magnitude of the current flowing between a counter electrode of the potentiostat and said working electrode, said three electrodes configured to be immerged into said solution; and 
 a digital processing circuit having a digital to analog converter for generating said input signal and having an analog to digital converter for generating a digital value representative of the output signal; 
 wherein the digital processing circuit is configured to modify said input signal and said working potential so as to maintain said digital value representative of said output signal inside a predetermined range; 
 wherein the input signal potential is representative of the solution pH when said output signal is maintained inside said predetermined range. 
 
     
     
       6. The system according to  claim 3 , wherein said second circuit comprises:
 an operational amplifier having an input connected to said working electrode and an output providing said sensed current; and 
 a feedback resistance coupled between the input and output of the operational amplifier. 
 
     
     
       7. The system according to  claim 6 , where said processor is further configured to control selection of a resistance value for said feedback resistance. 
     
     
       8. The system according to  claim 7 , wherein said resistance value is selected to avoid saturation of the operational amplifier. 
     
     
       9. The system according to  claim 3 , wherein said range is external to zero such that a redox state of the electro-conductive solid polymer transducer is modified by a current flow. 
     
     
       10. The system according to  claim 8 , wherein said output of the second circuit oscillates inside a predetermined range set by selection of the resistance value, the amplitude and phase of said output oscillation being indicative of the electrochemical impedance of said electrode cell. 
     
     
       11. The system according to  claim 5 , wherein said range is centered on zero. 
     
     
       12. The system according to  claim 5 , wherein the working electrode is made of polyaniline or polypyrrole. 
     
     
       13. The system according to  claim 5 , wherein said predetermined range is centered on zero. 
     
     
       14. The system according to  claim 13 , wherein said potentiostat comprises an operational amplifier having an input connected to said working electrode, the operational amplifier output generating said output signal and said operational amplifier being mounted in parallel with a resistance for acting as a current to voltage converter scaled by said resistance, said resistance being high or infinite to limit the current by saturation of the operational amplifier. 
     
     
       15. The system according to  claim 14 , wherein said resistance is modified in a range avoiding saturation of the operational amplifier and said output signal predetermined range is external to zero such that the redox state of the electro-conductive solid polymer transducer is modified by a current flow. 
     
     
       16. The system according to  claim 14 , wherein said resistance is modified in a range avoiding saturation of the operational amplifier so that said output signal oscillates inside said predetermined range, the amplitude and phase of said oscillations being indicative of the electrochemical impedance of said electrochemical cell. 
     
     
       17. The system of  claim 5 , wherein the electro-conductive solid polymer transducer is sensitized by a proton releasing enzyme mediator. 
     
     
       18. The system according to  claim 17 , wherein the proton releasing enzyme mediator comprises a β-lactamase enzyme.